Being a good witness can be helping out and can be the most beneficial of possible steps that could be taken. They're not mutually exclusive. Depends wholly on the scenario and what options are reasonable. Blindly jumping into the fray on principle merely to become a statistic does noone but the BG(s) any good.
I don't pretend to be Captain America. Given my skills, fitness and training, I have certain things I can and cannot do, but with clear limitations (nerve damage/injury). That affects a lot of my choices.
That said, I'll do what I'm able. That was a commitment I made in 1995 when I began carrying.